Heat islands surrounded on all sides by perspiration

Friday

Jul 13, 2012 at 12:01 AM

There is not a single tree on Jim Lewallen's block. Looking east down Main Street, he spots a towering palm perhaps three blocks away. To the west, he can make out the forested grounds near the county courthouse.

Alex Breitler

There is not a single tree on Jim Lewallen's block. Looking east down Main Street, he spots a towering palm perhaps three blocks away. To the west, he can make out the forested grounds near the county courthouse.

"It's pretty hot, and the reason is there's so much concrete around here. Concrete on the ground, concrete on the buildings, concrete all over the place," said Lewallen, 53, an artist who spent Thursday painting in the air-conditioned lobby of the Main Street Manor apartments.

Lewallen lives on an island of sorts, and it's too warm for his liking.

Downtown Stockton is hotter than surrounding neighborhoods and farmland.

You can probably feel the difference when you're driving into or out of the city, especially in the early evening, when coolness spreads more quickly over the green farm fields and Delta waters outside Stockton, while the concrete and asphalt urban center still smolders.

It's no trick of the mind.

And it's no joke, either. Urban "heat islands" pump up demand for energy, forcing residents to pay more to keep their air conditioners cranking. The extra heat also adds to the San Joaquin Valley's already woeful pollution levels. And for some, it can be deadly.

An Environmental Protection Agency study found that major cities are anywhere from 2 degrees to 5 degrees warmer than surrounding rural areas. At night, the difference can climb as high as 22 degrees.

No scientist appears to have ever measured Stockton's heat island. While it's likely not as severe as those larger cities, one leading expert says downtown Stockton is probably at least 1 degree to 2 degrees warmer than the rest of the region.

Anyone who has walked across a blacktop surface on a 100-degree day knows why. Pavement and dark-shaded structures absorb heat. When air moves into the area, instead of cooling over grass or water, it roasts over city streets and swirls into the "canyons" between buildings, where it cannot escape.

Night brings some relief but fails to offset all the heat that collects during the day.

And so the islands grow hotter and hotter as long as any given heat wave continues.

This week's heat wave should break today, with temperatures dipping back into the 90s. But in the long term, urban heat islands may grow more severe as cities such as Stockton expand outward, replacing farms and open land with more pavement and more rooftops.

It is another consequence of sprawl, said Arthur Rosenfeld, a professor emeritus of physics at the University of California, Berkeley, and a leading expert on urban heat islands.

Case in point: Los Angeles, where endless outward growth has pushed the city's core temperature up 7 degrees over the past 60 years.

"Every city in the world is getting hotter as it grows, with the single exception of Palm Springs, which is cooled by the golf courses," Rosenfeld said. "Los Angeles is going up 1 degree every 8 years, which is faster than global warming. This is more life-threatening than global warming."

And the lives that are threatened are primarily those of inner-city residents who are often poorer and perhaps more elderly than those in cooler suburbs, he said.

Then there's air pollution. On Wednesday, at the peak of this week's heat wave, every monitoring station from Stockton to Bakersfield recorded violations of the federal standard for harmful ozone (smog).

Ozone forms when pollutants from vehicle tailpipes, factories and other sources mix in the atmosphere and cook under a hot summer sun. The dome of heat encapsulating Valley communities aids that process.

It's a serious enough problem that the Valley Air Pollution Control District last year issued guidelines to help cities simmer down. The guidelines encourage building "cool roofs" or white roofs that reflect heat instead of absorbing it, and planting more trees.

As for trees, insolvent Stockton has had enough trouble maintaining the existing urban forest, not to mention expanding it.

Trees provide more than shade. They also cool the atmosphere by "sweating" water into the air. According to a paper by Rosenfeld, one properly watered tree can release 40 gallons of water per day, cooling the atmosphere enough to offset the equivalent of 100 brightly blazing light bulbs.

Lewallen worries about people, especially the elderly, who live in his downtown neighborhood and perhaps don't have air-conditioned lobbies in which to spend the hottest days of the year.